1. General
This invention relates generally to an analog/digital data device, and more particularly to a system and a method whereby communications between various pieces of Data Terminal Equipment (DTE) are effectuated in a error-free manner over both analog and digital networks.
At the Present time, the majority of the telephone networks operate in an analog fashion by utilizing electromagnetic waves to transmit messages, whereas computer systems operate in a digital fashion. Therefore, in order for one computer or DTE to communicate with another computer or DTE over distances where physical and permanent interconnection is impractical, the analog telephone lines are utilized. To effectuate the translation of digital signals to analog signals which the analog telephone system can handle, modems are well known in the art to be used to translate the signal from digital to analog in the form of electromagnetic waves (from the sending computer or DTE) using a modem connected to the sending DTE, transmitting the electromagnetic waves along the POTS (Plain Old Telephone System). The analog signals then enter a second modem which translates the analog signals back into digital signals and then to the receiving DTE or computer.
It is planned to gradually transform the present analog, electromagnetic wave-driven system to a pure digital system under the ISDN (Integrated Services Digital Network) standard. ISDN is specified by the CCITT I.series Recommendations. In such a system, when it is implemented, modems will no longer be needed because there will be no analog "leg" for which translation from digital to analog and back again from analog to digital is required.
However, it is most likely that the total transition from analog to digital will not take place either in the very near future nor at once when it does occur. Therefore, there will be a time period during which the analog and digital worlds will coexist, and equipment will be necessary to bridge the two worlds efficiently and effectively. This equipment will be required to allow the establishment of voice/data calls between users in an ISDN network and users in an analog network.
2. Description of the Prior Art
The technology exists today to establish voice calls between users in an ISDN network and users in an analog network. When a voice call is established, the telephone network, transparent to the user, automatically handles connections crossing the ISDN/analog network boundary. A user placing a voice call doesn't need to know that the call will cross the ISDN/analog network boundary. This is not the case when a data call is placed. The difference, of course, is that the data call is digital, not analog.
In the ISDN network, modems are not required, such that once a call is established between two DTE devices in the ISDN network, digital data is transferred in a digital format across the ISDN network.
In the prior art, one method for a user in the ISDN network to transfer data to a user in the analog network is to convert the data from digital to analog format at ISDN/analog network boundary. Several ISDN switch manufacturers use this method to provide data connectivity to the analog telephone network in which the digital to analog conversion is performed by modem pools. An ISDN user may establish a data call to a destination within the analog telephone network by first establishing a data call between the Terminal Adapter (TA) attached to the DTE device and the TA within the modem pool. Once the call between the two TAs has been established, the user must instruct the modem within the modem pool to establish a connection through the analog telephone network to the modem attached to the DTE at destination of the call. This two stage dialing process is cumbersome to a user on the ISDN network.
An analog user may establish a data call to a destination within the ISDN network, by first establishing a call between the modem attached to the DTE device and the modem in the modem pool. Once the connection between the modems is made, the user then instructs the second TA in the modem pool to establish a data call through the ISDN network to the first TA attached to the DTE at destination of the call. Again, this two stage dialing process is cumbersome to a user in the analog network.
At least one ISDN switch manufacturer is allowing users on the ISDN network to register two phone numbers with the ISDN switch. The first number is used by other users in the ISDN network to establish data calls with this device. The second number would be used by users in the analog network to establish data calls with this ISDN user. When the user in the analog network dialed the second telephone number, the data call would automatically be routed to the Modem in the Modem Pool. Once the connection between the modems was established, the ISDN network would automatically establish the connection between the second TA and the first TA. This would all be done transparently to the user in the analog network. Although this seems very convenient to the analog user, it becomes a management problem for the ISDN user.
Each time the ISDN user moves, he must register two numbers with the ISDN network. One for data calls from other ISDN users and one for data calls from user in the analog network. When giving out his phone number to a new user, he must check to see which network the new user is located on. It is much simpler for the ISDN user to deal with a single telephone number. Further, the ISDN/analog network boundary will be constantly changing as new sites receive ISDN service.
Once the data connection between the ISDN user and the analog user has been established, it should be noted that this connection is not a reliable, error-free, connection. While the ISDN protocol software can provide a reliable, error free connection between the first TA and the second TA, the RS-232 interface between the second TA and modem is not error-free. Parity, framing and flow control errors can occur at this interface which can corrupt user data. The connection between the first modem and the second modem may be a reliable, error-free connection provided that both modems implement an error-correcting protocol.
It is a principal object of the present invention to provide a data system and method in which communication may be established between a device at the S/T interface and a modem in the analog telephone network transparent to the ISDN and analog users.
Another object of the present invention is to provide a reliable, error free, data connection between ISDN and analog network users.